This invention relates to methods of improving uniformity of liquid deposition and to substrate coating. The invention also relates to substrate coating apparatuses.
In some applications, it can be desirable to form a uniform coating over a non-circular substrate. For instance, it can be desirable to coat a uniform layer of photoresist on a square or rectangular shaped radiation patterning tool, such as, for example, a reticle or mask.
One method of coating a radiation patterning tool is to spin the radiation patterning tool while flowing a liquid thereover. The liquid is commonly applied to the center of the radiation patterning tool and concentrically spreads outward in radial directions due to the action of centrifugal forces during spinning. A difficulty in utilizing the above-described spin coating method for applying liquid over non-circular shaped substrates (such as rectangular substrates) is that the non-circular periphery of the substrates can cause turbulent airflow during spinning that affect the uniform flow of the liquid. The turbulent airflow exerts undesirable aerodynamic forces to the liquid, causing non-uniform flow of the liquid on the substrate. Such can cause the thickness of the liquid to vary across the substrate.
In an exemplary process wherein a liquid photoresist is spun over a non-circular radiation patterning tool, the uneven distribution of the liquid can diminish the accuracy with which the photoresist is subsequently patterned. Such diminished accuracy of photoresist patterning can in turn lead to diminished accuracy in subsequent patterning of the radiation patterning tool. It would, therefore, be desirable to develop improved methods for spin coating non-circular substrates.
In one aspect, the invention includes a method of improving uniformity of liquid deposition when a liquid is spin-coated over a non-circular substrate. The substrate is retained on a platform and spun. The circular platform includes a plurality of shaping members pivotally connected to the platform. The plurality of shaping members are biased by spinning the platform to form a platform surface with a circular periphery.
In another aspect, the invention includes a method of coating a non-circular substrate. The substrate is secured to a support and spun. A plurality of shaping members are positioned proximate the non-circular substrate to form a circular surface. While spinning, the non-circular substrate is coated over with a photoresist material, and then the photoresist is patterned. After patterning the photoresist, the non-circular substrate is etched to form a radiation patterning tool with at least one opening.
In yet another aspect, the invention includes a substrate coating apparatus. Such apparatus comprises a non-circular substrate support configured to support a substrate with a planar surface and non-circular periphery. The apparatus further comprises a motor configured to spin the substrate support. A plurality of shaping members are pivotally connected with the substrate support and each shaping member has a curved outer side surface. Gravity biases the shaping members downward until an angular velocity of the substrate support provides a force to bias each shaping member upward adjacent the substrate to establish a circular surface.